Technology is already known in the art for saving energy by providing a power supply switch between the main power supply line and the circuit block included in macro cells, to turnoff the power supply switch during standby mode where the applicable circuit block is not operating in order to reduce the leakage current during standby mode.
Japanese Unexamined Patent Application Publication No. 2007-258226 discloses technology that provides an undefined output preventer circuit in the RAM block output stage for preventing through-current from flowing in the circuit blocks coupled to the RAM block that shuts off the power supply due to a floating state in the RAM block output for power shutdown caused by shutting off the power. Circuits provided in the output stage for preventing through-current such as undefined output preventer circuits are called isolation circuits.